The present invention relates to the operation of a metallurgical smelting furnace, particularly of the electro-plasma type, or more generally of the type in which the content of the furnace is heated by the development of primary energy. The smelting furnaces of the type to which the invention pertains require frequently that following the completion of the smelting process, the metal be removed without any inclusion of slag. In this regard, it has been suggested to discharge the molten metal eccentrically and from the bottom of the furnace upon opening a suitable closing device so that the molten metal can flow down in vertical direction. The discharge may be controlled by means of tilting the furnace. Alternatively, the discharge may occur centrally without tilting.
The discharge of a smelting furnace from the bottom of the vessel should occur in a laminar or near laminar flow. However, the mere discharge by means of pouring the molten metal out of the furnace does usually not suffice for preventing the outflow of slag nor is it sufficient to avoid particularly the mixture of slag with the pure molten metal. This is particularly due to the development of an eddy in the pouring flow that sucks slag into the outlet. Therefore, it is usually required to provide for specific steps that prevent the outflow of slag.
In the case of a tiltable furnace this prevention is obtained by a controlled tilting operation to thereby interrupt temporarily the discharge whenever slag is about to be commingled with the pure metal. It is apparent that the molten metal must be free from slag, particularly in cases in which subsequently casting or other refining-type treatment is provided for. Also, the prevention of slag inclusion is important as generally one operates with a liquid sump and uses scrap or scaly iron as charge. On the other hand, it can readily be seen that the interruption of the discharge in the manner described above means an interruption of the discharge process as a whole while particularly during periods of discharge flow the inclusion of slag is not preventable per se. In particular, the overall operation of the furnace discharge process is not of immediate relevancy nor of direct influence upon the flow pattern in the interior of the furnace vessel such that slag will or will not be included in the outpouring flow thereafter.
German printed patent application No. 18 04 007, suggests that the smelting furnace should be discharged only, i.e. the discharge process should begin only when the closure is, in fact, open in an extreme tilting position. This procedure assumes that a slag-free outpour will develop in this particular position of the furnace, but does not consider the interplay between the overall flow pattern of the molten metal within the furnace once the flow has begun in relation to the present distribution of the slag and the potential conditions for inclusion of slag particles in that flow. In other words, this method assumes certain statistical relations without consideration of basically unforeseen details in the flow pattern.
German printed patent application No. 29 44 269, suggests a particular configuration of the furnace cavity wherein a particular extension establishes a subcavity which communicates with the furnace interior at large by means of a flow passage arranged laterally near the bottom of the pan-shaped portion of the furnace interior. In this fashion, the metal is separated in this extension from the slag by means of a closure body floating in the metal bath such that a slag-free removal is, in fact, rendered dependent upon the presence and particular function of that floating closure body. However, the discontinuance of the discharge will prevent outflow of slag only towards the end of a pass in order to avoid a more significant disadvantage. As far as is known, no feature or concept is known at this point which prevents the outflow of slag in a comparable manner prior to the termination of the discharge pass of molten metals.